Carbon nanotubes composed of only carbon atoms (hereinafter referred to as CNT) are a material having excellent thermal conductivity, electrical properties and mechanical properties. The CNT is lightweight and very strong and is a material having excellent elasticity and recovery properties. The CNT having these excellent properties as described above is an attractive material, and very important as an industrial material.
Since the CNT is synthesized as an aggregate in general, in order to use the CNT in various applications it is necessary to loosen the carbon nanotube aggregate (hereinafter called CNT aggregate) after synthesis, and process mold into a desired shape. However, because CNT pairs have a strong van der Waals force, mutual CNTs are easily adsorbed to each other and cannot be easily loosened once adsorbed.
A CNT aggregate having such strong van der Waals forces is conventionally loosened using ultrasonic waves. In Japanese Laid-Open Patent Publication No. 2005-97029, after immersing a composition containing carbon nanotubes in a liquid and before separately collecting a solution containing a large amount of carbon nanotubes and a solution containing a large amount of components other than carbon nanotubes contained in a composition which contains carbon nanotubes, a stirring process, ultrasonic process, and centrifugation process are performed, and it is possible to improve the purification efficiency of the carbon nanotubes.
However, when the CNT aggregate is loosened by as ultrasonic waves, there is a problem in that the CNT breaks or is damaged and thus the CNT inherent characteristics cannot be sufficiently maintained. Conversely, when the CNT aggregate is loosened so as not to damage the CNTs, there is a problem in that the CNTs aggregate and a stable dispersion liquid cannot be obtained.
Many techniques for loosening the CNT have been reported. For example, in order to separate the CNTs more uniformly, in Japanese Laid-Open Patent Publication No. 2009-149832, after processing a mixed product of 10 mg of a double-walled CNT aggregate, 30 mg of Sodium polystyrene sulfonate and 10 mL of water using an ultrasonic homogenizer and performing centrifugation at 20000 G, when 9 mL of the supernatant was sampled, a CNT aggregate with a contained amount of CNTs in the supernatant of 0.6 mg/mL or more is used as the material of a transparent conductive film.
In addition, by using an aprotic organic dispersion medium and a wholly aromatic polyamide as aggregation inhibitors, in Japanese Laid-Open Patent Publication No. 2007-169120, a CNT dispersion liquid is disclosed in which bundles where no single-walled CNTs are formed or a bundle with very few single-walled CNTs exists stably.
However, even when these methods are used, it is difficult to obtained a CNT dispersion liquid or molded product in which there is very small damage to the CNT, while maintaining thermal conductivity and electrical properties, excellent mechanical properties of the CNT, high dispersibility and CNT dispersion stability, and is a factor that prevents the practical use for a variety of applications of the CNT.